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              <p class="title">IPS File Format</p>
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					<p><b>IPS specifications.</b><br>
					IPS format was created a lot of time ago and so the specs for many people are too restrictive for the modern needs.
					Well, let see these specs.</p>
					<ul>
						<li>IPS files can patch every file not larger than 2^24-1 bits (2047 Mb)</li>
					   <li>Every patch should not be larger than 2^16-1 bits (7.99 Mb)</li>
					   <li>An
IPS file can hold as many patches he can, assumed that the specified
offset and the size of every single patch doesn't overflow the
specified bounds.</li>
					</ul>
					<p>As you should realize it isn't so restrictive... 8 )</p>
					<p><b>IPS file format</b><br>
					The IPS file structure is made just like that:</p>

					<table bgcolor="#000080" border="0" width="100%">
					<tbody><tr>
						<td bgcolor="#800080" width="32%"><font color="#ffffff" size="2" face="Arial"><b>Section</b></font></td>
					   <td bgcolor="#800080" width="33%"><font color="#ffffff" size="2" face="Arial"><b>Size (Bytes)</b></font></td>
					   <td bgcolor="#800080" width="85%"><font color="#ffffff" size="2" face="Arial"><b>Description</b></font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="32%"><font color="#800080" size="2" face="Courier New">Header</font></td>
					   <td bgcolor="#ffffff" width="33%"><font size="2" face="Arial">5</font></td>
					   <td bgcolor="#ffffff" width="85%"><font size="2" face="Arial">The header show ever the same string: </font><font color="#800080" size="2" face="Courier New"> PATCH</font><font size="2" face="Arial"> note that the string is not NULL terminated.</font></td>
					</tr>
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					   <td bgcolor="#ffffff" width="32%"><font color="#800080" size="2" face="Courier New">Record</font></td>
					   <td bgcolor="#ffffff" width="33%"><font size="2" face="Arial">3+2+Variable</font></td>
					   <td bgcolor="#ffffff" width="85%"><font size="2" face="Arial">It's the record of a single patch, see below</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="32%"><font color="#800080" size="2" face="Courier New">....</font></td>
					   <td bgcolor="#ffffff" width="33%">&nbsp;</td>
					   <td bgcolor="#ffffff" width="85%"><font size="2" face="Arial">The numbers of record may vary</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="32%"><font color="#800080" size="2" face="Courier New">End Of file marker</font></td>
					   <td bgcolor="#ffffff" width="33%"><font size="2" face="Arial">3</font></td>
					   <td bgcolor="#ffffff" width="85%"><font size="2" face="Arial">A string (not NULL terminated) saying </font><font color="#800080" size="2" face="Courier New"> EOF</font></td>
					</tr>
					</tbody></table>
					<p><b>IPS Record structure:</b></p>
					<table bgcolor="#000080" border="0" width="100%">
					<tbody><tr>
						<td bgcolor="#800080" width="22%"><font color="#ffffff" size="2" face="Arial"><b>Section</b></font></td>
					   <td bgcolor="#800080" width="25%"><font color="#ffffff" size="2" face="Arial"><b>Size (Bytes)</b></font></td>
					   <td bgcolor="#800080" width="53%"><font color="#ffffff" size="2" face="Arial"><b>Description</b></font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="22%"><font color="#800080" size="2" face="Courier New">Offset</font></td>
					   <td bgcolor="#ffffff" width="25%"><font size="2" face="Arial">3</font></td>
					   <td bgcolor="#ffffff" width="53%"><font size="2" face="Arial">The offset where the patch will be placed in the file to patch</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="22%"><font color="#800080" size="2" face="Courier New">Size</font></td>
					   <td bgcolor="#ffffff" width="25%"><font size="2" face="Arial">2</font></td>
					   <td bgcolor="#ffffff" width="53%"><font size="2" face="Arial">The size of the data to put from the specified offset in the patching file</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="22%"><font color="#800080" size="2" face="Courier New">Data</font></td>
					   <td bgcolor="#ffffff" width="25%"><font color="#800080" size="2" face="Courier New">Size</font></td>
					   <td bgcolor="#ffffff" width="53%"><font size="2" face="Arial">Contains a number of Size bytes of data to be copied in the file to patch </font></td>
					</tr>
					</tbody></table>
					<p>And that's the info you can find around. Now the technical stuff and RLE infos.</p>
					<p><b>IPS RLE encoding</b><br>
					The next big step in the comprehension of the IPS format is that some patches can be RLE encoded to save space. The
					encoding is very simple but can easily be overlooked if someone is not aware of that. If when you read the size value
					of a record this field contains 0 you have a RLE encoded patch. You should read again a 16 bit value to obtain the size
					of the RLE patch and then you should read a single byte. This byte must be repeated as many times as the value of the
					second 16 bit read. An IPS RLE Record should look like that:</p>
					<p><font color="#000080" size="2" face="Arial">IPS RLE Record structure:</font></p>
					<table bgcolor="#000080" border="0" width="100%">
					<tbody><tr>
						<td bgcolor="#800080" width="28%"><font color="#ffffff" size="2" face="Arial"><b>Section</b></font></td>
					   <td bgcolor="#800080" width="26%"><font color="#ffffff" size="2" face="Arial"><b>Size(Bytes)</b></font></td>
					   <td bgcolor="#800080" width="100%"><font color="#ffffff" size="2" face="Arial"><b>Description</b></font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="28%"><p><font color="#800080" size="2" face="Courier New">Offset</font></p></td>
					   <td bgcolor="#ffffff" width="26%"><font size="2" face="Arial">3</font></td>
					   <td bgcolor="#ffffff" width="100%"><font size="2" face="Arial">Any Value</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="28%"><font color="#800080" size="2" face="Courier New">Size</font></td>
					   <td bgcolor="#ffffff" width="26%"><font size="2" face="Arial">2</font></td>
					   <td bgcolor="#ffffff" width="100%"><font size="2" face="Arial">0</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="28%"><font color="#800080" size="2" face="Courier New">RLE_Size</font></td>
					   <td bgcolor="#ffffff" width="26%"><font size="2" face="Arial">2</font></td>
					   <td bgcolor="#ffffff" width="100%"><font size="2" face="Arial">Any nonzero value</font></td>
					</tr>
					<tr>
					   <td bgcolor="#ffffff" width="28%"><font color="#800080" size="2" face="Courier New">Value</font></td>
				      <td bgcolor="#ffffff" width="26%"><font size="2" face="Arial">1</font></td>
					   <td bgcolor="#ffffff" width="100%"><font size="2" face="Arial">This is the value to write </font><font color="#800080" size="2" face="Courier New">RLE_Size</font><font size="2" face="Arial"> times starting from Offset</font></td>
					</tr>
					</tbody></table>
					<p>&nbsp;</p>
					<p><b>Encoding Of Offset and Size</b><br>
					For peoples using low level languages a little bytes-swapping is needed to make read right the values of Offset and Size.
					These values are written linearly, just like Pascal and Basic does when handling numerical variables. The problem is that
					low level languages like ASM and C/C++ use the same endianess format of the machine, so every couple of two bytes are
					swapped. A 16 bit value is written like this in the IPS: 0x6712, a 24 bit value in this way: 0x671234. If read with a low
					level language they'll throw up: 0x1267 and 0x341267 respectively. Here two C macros that does
					the conversion after you read them. bp should be a char array:</p>
					<p><font size="2" face="Courier"><font color="#800080">#define BYTE3_TO_UINT(bp)   \<br>
					&nbsp;&nbsp;&nbsp;&nbsp; (((unsigned int)(bp)[0] &lt;&lt; 16) &amp; 0x00FF0000) | \<br>
					&nbsp;&nbsp;&nbsp;&nbsp; (((unsigned int)(bp)[1] &lt;&lt;  8) &amp; 0x0000FF00) | \<br>
					&nbsp;&nbsp;&nbsp;&nbsp; ((unsigned int)(bp)[2] &amp; 0x000000FF)<br><br>
					#define BYTE2_TO_UINT(bp)   \<br>
					&nbsp;&nbsp;&nbsp; (((unsigned int)(bp)[0] &lt;&lt; 8) &amp; 0xFF00) | \<br>
					&nbsp;&nbsp;&nbsp; ((unsigned int) (bp)[1] &amp; 0x00FF)</font></font></p>
					<p>16 bit compiler users may find useful to substitute <font size="2" face="Courier">unsigned int</font>
					<font size="2" face="Arial"> to </font><font size="2" face="Courier New">unsigned</font><font size="2" face="Arial">
					</font><font size="2" face="Courier New">long in&nbsp;</font><font size="2" face="Arial">
					the </font><font size="2" face="Courier New">BYTE3_TO_UINT</font><font size="2" face="Arial"> macro...</font></p>
					<p><font size="2" face="Arial">Real simple once someone has hacked the format for you, isn't it?</font></p>
      			<p align="right"><b><a href="mailto:z.e.r.o@softhome.net"><font color="#800080" size="3" face="Arial">Z.e.r.o</font></a></b></p>
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